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891.
892.
在滚石冲击破坏建(构)筑物灾害中,滚石形状往往具有不确定性,建(构)筑物表面形状也不尽相同。当滚石冲击结构物时,由于滚石形状的不同导致其所表现出来的冲击动力响应特征也不同。采用ABAQUS有限元软件中的Explicit动力有限元方法,分别开展不同形状滚石冲击不同表面形状结构物的数值模拟研究,并对不同缓冲层的缓冲耗能特性进行对比分析。结果表明:在质量、初速度相同的初始条件下,形状不同的滚石冲击平面墙状的结构物时,冲击力峰值大小依次为正方体>圆柱体(底面)>圆柱体(侧面)>球体>三棱锥;当滚石冲击面形状由“尖”变“钝”时,结构物受滚石冲击处被破坏程度将变小,但其整体变形区域增大;对不同表面形状的结构物承受滚石冲击时,冲击力峰值大小依次为平面状>凸面状>凹面状>波浪面状>斜面状,相比而言,斜面状结构物具有较好的抗滚石冲击性能;对在结构物前方设置不同缓冲层时对滚石冲击的缓冲耗能特性进行对比分析,得出EPS-砂土复合垫层具有较好的缓冲耗散性能,其在实际的滚石灾害防护工程中具有广阔的应用前景。 相似文献
893.
A method for estimating the gear shape of a mid-water trawl 总被引:2,自引:0,他引:2
894.
Understanding the formation and evolution of the soil and dust of the Moon addresses the fundamental question of the interactions of space with the surface of an airless body. The physical and chemical properties of the lunar dust, the <20 μm portion of lunar soil, are key properties necessary for studies of the toxicity and the electrostatic charging of the dust. These properties have been largely overlooked until recent years. Although chemical and physical studies of the <20 μm portion of lunar soil have been the topic of several studies, there is still need for further studies, primarily of the <1 μm particles. This paper presents a review of the studies of lunar dust that have been conducted to date. As many preparations for future exploration or science activities on the Moon require testing using lunar soil/dust simulants, we also include a brief review of past and current simulants. 相似文献
895.
针对北方地浸砂岩型铀矿超过400m钻孔钻进中弹塑性致密泥岩钻进效率低的问题,研究试验了钻头,提高了钻进效率,总结了操作技术。用φ104mm中八角阶梯肋骨钻头钻进较软弹塑性致密的光滑的红褐色、浅绿色“打滑”泥岩;用φ104mm中八角阶梯肋骨钻头钻进较软弹塑性致密的灰色致密泥岩;用φ104mm交错式圆片状复合片钻头钻进脆性较大的黑灰色弹塑性致密泥岩;用φ104mm交错式圆片状复合片钻头钻进灰白色脆性较大的弹塑性致密泥岩;用φ104mm双环式齿形复合片钻头钻进弹塑性致密硬泥岩。 相似文献
896.
897.
Many data sets can be viewed as a collection of samples representing mixtures of a relatively small number of end members. When end members are present in the sample set, the algorithm QMODEL by Klovan and Miesch can efficiently determine proportionate contributions. EXTENDED QMODEL by Full, Ehrlich, and Klovan was designed to deduce the composition of realistic end members when the end members are not represented by samples. However, in the presence of high levels of random variation or outliers not belonging to the system of interest, EXTENDED QMODEL may not be reliable inasmuch as it is largely dependent on extreme values for definition of an initial mixing polyhedron. FUZZY QMODEL utilizes the fuzzy c-means algorithm of Bezdek to provide an alternative initial mixing polyhedron. This algorithm utilizes the collective property of all the data rather than outliers and so can produce suitable solutions in the presence of noisy or messy data points. 相似文献
898.
Stephen E. White 《The Professional geographer》1985,37(1):28-35
The macro-level activity spaces of residents in Atlanta, Boston, Cleveland, Denver, Kansas City, and San Francisco differ significantly in areal extent, compactness and shape. They fail to conform closely with the pattern expected based on gravity formulations of distance to and size of potential destinations. Activity space is defined as the percentage of respondents in each city who have visited thirty other metro areas within a decade. Maps of residuals from regression indicate that the major visitation flows from each city are neither random nor concentric but spatially concentrated and easily identified. Macro-level activity spaces may be useful in understanding interregional migration flow bias. 相似文献
899.
Björn A. Malmgren 《Mathematical Geology》1976,8(2):165-182
The biserial planktonic foraminiferal species Heterohelix striata (Ehrenberg)has been analyzed by morphometric techniques from six sequential late Maestrichtian core samples from southern Sweden and one sample from the Daniaquarry of Denmark. The study is based on measurements of number of chambers, size of test (length, width, and thickness),marginal angle, and chamber sizes. In addition, prolocular and apertural sizes were analyzed in the Daniaquarry sample. The study includes analyses of the ontogenetic development of the tests, stratigraphic variation in size and shape, intrasample variability, and relationship between gross morphology of the test and prolocular and apertural dimensions. 相似文献
900.
黑龙江省砂金的粒度及形态特征 总被引:5,自引:3,他引:5
对黑龙江省79个砂金及3个岩金样品进行了粒度及形态研究,多数样品的平均粒径在0.3 ̄0.6mm之间,以正态分布为主,分选系数和磨圆度表明多为远距离搬运的砂金,通过金粒总体形态比较,将形态划分为4类,其中第一类为岩金,第二类为有利于在其附近寻找原生金矿床的残积金。 相似文献